Clouds on Martian Terminator: A Study Through the Images Captured by the Mars Colour Camera (MCC) During MY32 to 34

Abstract

The present study reports a cloud feature observed by the Mars Colour Camera (MCC) onboard India’s first Mars Orbiter Mission in both the Martian terminator during the MY 32 to 34: “The Twilight Cloud”. Twilight clouds used to show latitudinal expansion, covering over 5,000 km² and used to appear between 19:00 LT and 20:00 LT for evening and 04:00 LT and 05:00 LT for morning terminator. These clouds often reached altitudes of at least 15 to 40 km. We further compare these observations to Mars Climate Sounder (MCS) data. The TOA (Top of the Atmosphere) reflectance varies from 0.030 to 0.035 in the blue channel and 0.025 to 0.030 in the red channel indicates the presence of both dust and water ice at the observed altitude level. The MCD-GCM (Mars Climate Database Web Interface- General Circulation Model) simulations used to estimate the mixing ratio. MCS extinction data along with simulated MCD results, estimated the effective radius of the particle to be varying from 0.3 to 3.0 μm. The work also infers the seasonal behaviour of these clouds, especially during NHS (Northern Hemisphere Summer) and LNHA (Late Northern Hemisphere Autumn). The present work indicates that the daily thermal variation is one of the plausible reasons for the formation of the clouds.